What "Apple Proprietary Format?" AAC? That's an industry standard file format. Are you referring to the Music Industry's required Digital Rights Management (DRM) that Apple was instrumental in getting eliminated?
Apple ALWAYS allowed you to convert your music files to MP3 files. . . it was change in policy or ability of iTunes as you imply it was. . . you could even convert the DRMed files. .. . but because you were converting to MP3, you got a lesser quality sound. SHEESH!
Funny. I am not able to play any if the Apple formats on my non Apple devices. MP3 is the true industry standard and can be played on all devices.
Converting to MP3. Wrong! We’ll yes if you were okay with burning through a stack of CDs and ripping them back to MP3. A very time consuming and expensive process. A big pain in the arse. Now you can convert them directly to MP3 in itunes.
BTW you can choose the MP3 bit rate and think it can go higher than 200k. I chose 160K for sound quality vs disk space.
Bottom line: a song file is useless to me if I can’t play it on anything other than Apple device.